Sam Tanenhaus's essay "Conservatism Is Dead" prompted intense discussion and debate when it was published in The New Republic in the first days of Barack Obama's presidency. Now Tanenhaus, a leading authority on modern politics, has expanded his argument into a sweeping history of the American conservative movement. For seventy-five years, he argues, the Right has been split between two factions: consensus-driven "realists" who believe in the virtue of government and its power to adjust to changing conditions, and movement "revanchists" who distrust government and society-and...